<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button id="postBtn">post</button>

  <script>
    let postBtn = document.querySelector('#postBtn')

    postBtn.onclick = function() {
      // 1. xhr对象
      let xhr = new XMLHttpRequest()

      // 2. 先 open  设置请求头  再 send
      xhr.open('POST', 'http://www.liulongbin.top:3006/api/addbook')
      // post 设置请求头
      xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
      xhr.send('bookname=成都真好&author=张三&publisher=成都出版社')

      // 3. 事件监听
      xhr.onreadystatechange = function() {
        if(xhr.readyState === 4 && xhr.status === 200) {
          console.log( xhr.responseText )
        }
      }

    }
  </script>
</body>
</html>